CHAPTER 1
 GENERAL INTRODUCTION

 Examining the fluid flow of the deep hydrosphere is extremely important because

fluid flow alters the physical and chemical properties of the Earth's crust, which in turn

affects the ocean and the atmospheric chemistry that is vital for human existence

(COMPLEX, 1999). At active plate margins, fluid flow can influence movement along

faults and thus the nature of the earthquake cycle. Several research projects have recently

been focused on studying fluid flow along active plate margins. The Ocean Drilling

Program (ODP) has contributed valuable information on fluid behavior by sampling the

sediments and oceanic crust at shallow ends of the subduction zones.

 At convergent margins, the incoming sediments and lithosphere are fed into the

subduction factory where processes such as compaction and dewatering, diagenesis,

dehydration, metamorphism, melting, melt migration and mantle convection result in

hazardous seismicity, explosive volcanism as well as the formation of ore deposits and

new continental crust (Moore, 1998). A large number of the world's greatest earthquakes

are associated with subduction zones. A small portion of the plate contact, known as the

seismogenic zone, is responsible for generating these large earthquakes. Understanding

the processes of the seismogenic zone provides valuable information on earthquake

generation, but requires studying many aspects of geology.

 Shallowly dipping subduction zones provide a large fault surface that is accessible

to study by allowing sampling of the incoming sediments. In such localities, accretionary

complexes are formed if sediments are scraped off the subducting oceanic plate and